1. Field of Use
The process of this invention relates to a process for removing lower alcohols from a tetrahydrofuran stream. More particularly, the process of this invention relate to a process for removing lower alcohols from a tetrahydrofuran stream by extractive distillation with water.
2. Prior Art
In the production of tetrahydrofuran (THF) from acetylene and formaldehyde, crude 1,4-butanediol (BAD) is heated in a cyclization reactor in the presence of sulfuric acid to cyclize the BAD to form THF with water and small quantities of methanol. The THF and water produced are vaporized from the cyclization reactor through a distillation column with the small quantities of methanol. However, in the process of dehydrating the THF the amount of methanol tends to build up in the system due to the formation of a low boiling binary azeotrope between methanol and THF which is not readily separable by direct distillation. Methanol can be removed or reduced by means of a purge. Purging, to remove the methanol cannot be achieved without a loss of THF. It is estimated that for every pound of methanol removed from the system some 5 to 10 pounds of THF are lost.
BAD can also be produced by hydrogenation of a mixture of formyl acetals containing, for example, 2-.beta.-formylethyl-5-methyl- 1,3-dioxane. The product of said hydrogenation includes BAD, an aqueous byproduct mixture of lower alcohols and THF. This alcohol mixture may contain methanol, ethanol, normal propanol and normal and iso butanol. Recovery of a substantially pure THF-water azeotrope from this mixture is desirable. The separatin of n-propyl and the normal and isobutyl alcohols can be accomplished by direct distillation, but in the case of methanol and ethanol, due to azeotrope formation, separation cannot be made by direct distillation.
In the manufacture of polybutylene terephthalate resins by reaction of BAD with the methyl ester of the terephthalic acid, methanol and THF are formed. An efficient procedure is needed to separate THF and methanol.
U.S. Pat. No. 2,198,651 discloses a process for the separation of constant boiling ternary mixtures of an alcohol, acetone and an unsaturated compound(s) whereby two binary mixtures are formed. A ternary mixture disclosed is methanol, acetone and tetramethylene oxide (THF). In all mixtures disclosed, acetone is present. The scope of the disclosure and teaching is therefore limited to ternary mixtures containing acetone. Acetone is a known entrainer for THF in a wet system. In such a system, acetone would be taken overhead with the THF and thus be an undesirable contaminant.